My present invention relates to a method of producing elongated drop-forged articles and, more particularly, to a method of operating a forge for the production of such articles utilizing hot deformation in a vertical fully automatic forging press having a plurality of successive or adjacent tool stages between which the workpiece is displaced by a transfer system.
Drop-forging processes which have dies or tools forming a multiplicity of forging stages and between which workpieces can be transported by a transport system as a rule utilize a walking beam transport or transfer system and can have these tool stages arranged in succession in a direction of stepping of the workpieces between the stages. In general, the tools are spaced within the press with a constant center-to-center distance and a single die represents each of the forging stages for graded shaping of a workpiece. In the production of drop-forged articles utilizing such presses, two modes of operation have become common. In a first mode of operation the individual tool stages are charged with a workpiece every second press stroke and each other stage remains ineffective during that stroke but receives the workpiece in the next press stroke. In this operation, a product is produced every second press stroke.
In another mode of operation, the workpieces are stages so that each stage receives a workpiece at each stroke and in that case, a product is outputted with each stroke.
Elongated articles and workpieces generally utilize rectangular dies which have relatively small widths in proportion to their length. These dies can be mounted directly adjacent one another in the die holder of the press. The shorter widths of the dies lie adjacent one another in the press. In such presses, five or six tool or die stages can be provided alongside one another.
The elongated forges can be levers, cam shafts, connecting rods and fittings widely used in the automotive field and for engines and the like. It is important that the final product be predominantly free from sharp edges, depressions or markings as can be produced if the die is provided with ejectors or the like. For that reason as well, the die cavities for such workpieces should be flush with one another where the upper and lower part of the die adjoin. It is also a common practice to fabricate such parts in pairs. For example, for crankshafts for internal combustion engines or multiple forgings in the case of fittings, two or more articles may be forged together while being interconnected in a common forging die.
The dies themselves may be fabricated with great precision by CNC machining methods and these methods and copier milling permit multiple cavity dies to be fabricated in the same time as individual cavity dies and with such precision that the die parts are flush with one another. Once these double or multiple workpieces are fabricated, they can be separated from one another by removal of the flashing between them.
The parts which are fabricated in this manner may have a relatively large surface area to weight ratio.
As a consequence, with increasing press frequencies or cadence, the heat transfer from the hot workpiece to the die can be substantial since, all other things being equal, the heat transfer from the workpiece to the die is a function firstly of the cadence of operation of the press, then the residence time of the article in contact with the die parts, the temperature drop between the workpiece and the tool and the contact area of the workpiece with the tool.
As a consequence with higher cadences, higher degrees of cooling of the die may become necessary and that, in turn, requires the forcing of greater quantities of the coolant/lubricant through the die. In the absence of the greater degree of cooling, the die may heat up excessively and that can lead to failure of the forging tool.
Of course, the use of excessive cooling lubricant can be a problem as well since the liquid may not evaporate uniformly over the entire area of the workpiece enclosed in the die. As a result the liquid may not be able to flow away and may tend to be forced out through gaps in the die. This can result in irregular shaping of the workpiece, premature damage to the die by erosion and cracking, and problems with the product.
Because of these factors, the press operations have been limited to cadences such that three to four seconds were required for each outputted product and hence relatively low production rates. Any effort to increase the output in the past has resulted in shorter die life or could be applicable only in the case of small articles with reduced surface area.
It is, therefore, the principal object of the present invention to provide an improved method of forging a workpiece or, more specifically, of operating a forge for the production of elongated articles as described whereby it is possible to operate the press with a cadence or frequency of two seconds per workpiece or less and thus a substantially higher cadence for reduced periods than has hitherto been the case and without difficulty, thereby increasing the output of the press.
Still another object of this invention is to provide a method of operating forging stages and die sets, i.e. tools, between which the workpieces are moved by a transporter, whereby drawbacks of earlier forging systems are obviated.
Still another object of the invention is to increase the output of a forging press without increasing die or tool wear or otherwise endangering the die or tool of the press.
These objects are attained, in accordance with the invention, by providing each forging stage with two identical adjacent dies or tools spaced apart by a center-to-center distance which is exactly half the transfer step of the transporter and whereby the two dies of each pair are utilized alternately and the unused die of the respective pair is thus permitted to cool until the die at the next press cycle is charged with a workpiece. Thus while each workpiece is advanced by a full step, the separation of successive die cavities by half of a full step ensures that each, by receiving a workpiece in one stroke of the press, is to be empty in the next stroke and each die which was empty at one stroke will receive a workpiece in the next stroke. As a consequence, while a workpiece is produced with each stroke of the press, at each press stroke half the dies remain unused and thus can be cooled.
A method of operating a forge according to the invention thus can comprise the steps of:
(a) providing a multiplicity of mutually adjacent forging stations for successive stages of forging of a heated elongated workpiece and a pair of substantially identical forging tools for each of said stages at a given spacing between the tools of each stage and a said given spacing of the mutually closest tools of adjacent stages;
(b) charging one of the tools of each stage with a respective workpiece so that corresponding tools of alternating stages are effective in forging said workpieces and another tool of each stage is simultaneously inoperative;
(c) advancing a new workpiece into said other tool of a first of said stages, advancing a forged article from said one tool of a last of said stages and advancing each workpiece in a stage up to said last of said stages from the one tool in each stage to the other tool of the next stage in an increment of advance equal to twice said given spacing; and
(d) thereafter advancing a further new workpiece into said one tool of said first of said stages, advancing a forged article from said other tool of said last of said stages and advancing each workpiece in a stage up to said last of said stages from the other tool in each stage to the one tool of the next stage in said increment of advance.
Thus while the successive dies are spaced apart by half the transport step and the workpieces are always displaced by a full transport step between the press strokes. Each full transport step is twice the center-to-center distance of the adjacent dies.
One important feature of the invention in the operation of a forge utilizing forging dies with widths which are comparatively small with respect to their lengths and simultaneously for the successive stages in the forging and utilizing simple forging dies (single workpiece dies) as well as multiple workpiece dies is that in spite of the fact that each die is used alternately, i.e. is employed for forging at one stroke and is not employed for forging at the next stroke, is that the output of the press is not halved.
Furthermore, it is not necessary to increase the press force of the press since the unused dies at each stage do not contribute to a utilization of the press force. Furthermore, a conventional beam or lifting beam transporter of conventional design can be used for transporting the workpieces through the system.
It is only necessary to equip the lifting beam transporter with twice the number of grippers or transport clamps and to space them at the center-to-center distance between the dies.
Thus where the cycling time of the press per workpiece has been say four seconds in the past, the press of the invention can operate with a cycling time of two seconds for each workpiece which means that the heat-transfer from each workpiece to the respective die is reduced to about 50% of the heat transfer which had previously to be accommodated.
According to the invention the transport steps of the transfer system is half the center-to-center distance between successive dies along the path and each tool stage of the press (formed by a pair of dies) only receives one workpiece. In the next transfer step, the die which has previously been unused of the next tool stage then receives a workpiece and the die thereof which previously held a workpiece is emptied during the forging stroke.
According to a feature of the invention, therefore, steps (c) and (d) of the method are repeated as many times as is necessary to forge the desired number of workpieces.
The invention also includes a forge for the production of elongated articles which comprises:
a multiplicity of mutually adjacent forging stations for successive stages of forging of a heated elongated workpiece and a pair of substantially identical forging tools for each of said stages at a given spacing between the tools of each stage and a said given spacing of the mutually closest tools of adjacent stages, whereby one of the tools of each stage can be charged with a respective workpiece so that corresponding tools of alternating stages are effective in forging said workpieces and another tool of each stage is simultaneously inoperative; and
a workpiece transporter engageable with said workpieces for simultaneously advancing a new workpiece into said other tool of a first of said stages, advancing a forged article from said one tool of a last of said stages and advancing each workpiece in a stage up to said last of said stages from the one tool in each stage to the other tool of the next stage in an increment of advance equal to twice said given spacing, and for thereafter simultaneously advancing a further new workpiece into said one tool of said first of said stages, advancing a forged article from said other tool of said last of said stages and advancing each workpiece in a stage up to said last of said stages from the other tool in each stage to the one tool of the next stage in said increment of advance.
The forge can be a walking or rising-beam conveyor which can be provided with grippers for engaging the workpieces.
Upstream of the first of the stages is a station for receiving new workpieces and which is configured to hold workpieces at the aforementioned given distance apart.
Each of the tools or dies is preferably configured to shape a pair of aligned elongated articles which may be automotive connecting rods.